Microencapsulated Catalyst-Ligand System

ABSTRACT

A microencapsulated catalyst-ligand system is provided comprising a catalyst and a ligand microencapsulated within a permeable polymer microcapsule shell, wherein the ligand is a polymeric ligand. Processes for the preparation of said microencapsulated catalyst-ligand system are also provided.

FIELD OF THE INVENTION

This invention relates to catalyst systems, in particular tomicroencapsulated catalyst systems and processes for their preparation.

BACKGROUND TO THE INVENTION

WO 03/006151 describes encapsulated catalyst systems and methods fortheir production. In particular, this publication describespalladium-based encapsulated catalysts that find use in couplingreactions. These palladium-based systems are most often derived bymicro-encapsulation of palladium acetate.

WO 2005/016510 describes a process in which a metal catalyst ismicroencapsulated in the presence of a ligand. This publicationdescribes that the use of a ligand may reduce catalyst leaching duringthe encapsulation process.

SUMMARY OF THE INVENTION

The present invention is based on a discovery that catalyst leachingfrom a microencapsulated catalyst-ligand system during use can bereduced using a polymeric ligand. Without wishing to be bound by theory,it is believed that polymeric ligands are bound tightly within thepolymer matrix of the microcapsule, thereby retaining the catalystwithin the microcapsule. This binding may arise through stericinteractions (such as chain entanglement or greatly reduced diffusionrates of larger molecules) or through chemical binding, such as ionic,electrostatic or covalent bonds formed by polymerisation with themicrocapsule shell or a constituent (e.g. a monomer or prepolymer)thereof.

According to a first aspect of the present invention there is provided amicroencapsulated catalyst-ligand system comprising a catalyst and aligand microencapsulated within a permeable polymer microcapsule shell,wherein the ligand is a polymeric ligand.

According to a second aspect of the invention there is provided aprocess for the preparation of a microencapsulated catalyst-ligandsystem, which comprises:

-   -   (i) forming a microcapsule shell by interfacial polymerisation        in the presence of a catalyst and a ligand;    -   (ii) forming a microcapsule shell by interfacial polymerisation        in the presence of a catalyst and treating the microcapsule        shell with a ligand; or    -   (iii) forming a microcapsule shell by interfacial polymerisation        in the presence of a ligand and treating the microcapsule shell        with a catalyst solution;        wherein the ligand is a polymerisable ligand and the process        further comprises polymerising the ligand prior to, during or        after formation of the microcapsule shell.

DESCRIPTION OF VARIOUS EMBODIMENTS Ligand

Microencapsulated catalyst-ligand systems of the invention comprise apolymeric ligand. Said systems may be obtained through a processinvolving polymerisation of a polymerisable ligand, i.e. a ligand whichis capable of undergoing polymerisation.

Various types of polymerisation are encompassed by the presentinvention. For example, the ligand may undergo self-polymerisation toform a polymer which is bound within the microcapsule shell by stericinteractions with the microcapsule matrix. Alternatively, the ligand maycopolymerise with another species, for example the microcapsule shell ora constituent (e.g. a monomer or prepolymer) thereof. The ligand maytherefore be in the form of one or more pendant groups bound to themicrocapsule matrix. Alternatively or additionally, the ligand maycopolymerise with another ligand type, to form a copolymeric ligandwhich may or may not be bound to the microcapsule matrix. The ligand maybe polymerised by any suitable polymerisation known in the art, forexample free radical, addition or condensation polymerisation.

The polymerisable ligand may be an organic ligand. Organic ligandstypically include organic moieties which comprise at least onefunctional group or heteroatom which can coordinate to the metal atomsof the catalyst. Organic ligands include mono-functional, bi-functionaland multi-functional ligands. Mono-functional ligands comprise only onefunctional group or heteroatom which can coordinate to a metal.Bi-functional ligands or multi-functional ligands comprise more than onefunctional group or heteroatom which can coordinate to a metal.

The organic ligand may be an organic moiety comprising one or moreheteroatoms selected from N, O, P and S.

In particular, the organic ligand may be an organic moiety comprisingone or more P atoms.

Of particular mention are organic ligands of formula (1):

PR¹R²R³  (1)

-   -   wherein:        -   R¹, R² and R³ are each independently an optionally            substituted hydrocarbyl group, an optionally substituted            hydrocarbyloxy group, an optionally substituted hydrocarbyl            group where one or more carbon atoms in the group are            replaced by a sulphur, oxygen or nitrogen atom, or an            optionally substituted heterocyclyl group or one or more of            R¹ & R², R¹ & R³, R² & R³ optionally being linked in such a            way as to form an optionally substituted ring(s); and        -   at least one of R¹, R² and R³ comprises a polymerisable            group.

Hydrocarbyl groups which may be represented by R¹⁻³ independentlyinclude alkyl, alkenyl and aryl groups, and any combination thereof,such as aralkyl and alkaryl, for example benzyl groups.

Alkyl groups which may be represented by R¹⁻³ include linear andbranched alkyl groups comprising up to 20 carbon atoms, particularlyfrom 1 to 7 carbon atoms and more particularly from 1 to 5 carbon atoms.When the alkyl groups are branched, the groups often comprise up to 10branch chain carbon atoms, in particular up to 4 branch chain atoms. Incertain embodiments, the alkyl group may be cyclic, commonly comprisingfrom 3 to 10 carbon atoms in the largest ring and optionally featuringone or more bridging rings. Examples of alkyl groups which may berepresented by R¹⁻³ include methyl, ethyl, propyl, 2-propyl, butyl,2-butyl, t-butyl and cyclohexyl groups.

Alkenyl groups which may be represented by R¹⁻³ include C₂₋₂₀, inparticular C₂₋₆ alkenyl groups. One or more carbon-carbon double bondsmay be present. The alkenyl group may carry one or more substituents,particularly phenyl substituents. Examples of alkenyl groups includevinyl, allyl, styryl and indenyl groups.

Aryl groups which may be represented by R¹⁻³ may contain 1 ring or 2 ormore fused rings which may include cycloalkyl, aryl or heterocyclicrings. Examples of aryl groups which may be represented by R¹⁻³ includephenyl, tolyl, fluorophenyl, pentafluorophenyl, chlorophenyl,bromophenyl, trifluoromethylphenyl, anisyl, naphthyl and ferrocenylgroups.

Heterocyclic groups which may be represented by R¹⁻³ independentlyinclude aromatic, saturated and partially unsaturated ring systems andmay constitute 1 ring or 2 or more fused rings which may includecycloalkyl, aryl or heterocyclic rings. The heterocyclic group willcontain at least one heterocyclic ring, the largest of which willcommonly comprise from 3 to 7 ring atoms in which at least one atom iscarbon and at least one atom is any of N, O, S or P. Examples ofheterocyclic groups which may be represented by R¹⁻³ include pyridyl,pyrimidyl, pyrrolyl, thiophenyl, furanyl, indolyl, quinolyl,isoquinolyl, imidazoyl and triazoyl groups.

Any of R¹⁻³ may further comprise one or more other substituents. In thiscase, the one or more other substituents should normally be selected soas not to adversely affect the activity of the catalyst or the abilityof the group to undergo polymerisation. Examples of suitable optionalsubstituents include halogen, cyano, nitro, hydroxy, amino, thiol, acyl,hydrocarbyl, perhalogentated hydrocarbyl, heterocyclyl, hydrocarbyloxy,mono or di-hydrocarbylamino, hydrocarbylthio, esters, carboxylate,carbonates, amides, sulphonate, sulphonyl and sulphonamido groups,wherein the hydrocarbyl groups are as defined for R¹ above. One or moresubstituents may be present, and includes when any of R¹, R² or R³ is aperhalogenated hydrocarbyl group. Examples of perhalogenated hydrocarbylgroups which may be represented by R¹⁻³ include —CF₃ and —C₂F₅ andpentafluorophenyl.

When any of R¹ and R², R¹ and R³, and R² and R³ are linked in such a waythat, when taken together with the phosphorus atom to which they areattached, a ring is formed, In this case, the ring is often a 5-, 6- or7-membered rings.

The ligand may be capable of undergoing free radical polymerisation. Theterm “free radical” as used herein includes reference to an atomic ormolecular species which contains an unpaired electron. Thus, the ligandmay comprise one or more atoms or groups which are susceptible to freeradical polymerisation. Of particular mention are organic ligandscomprising one or more of said atoms or groups. With regard to formula(1), at least one of R¹, R² and R³ may comprise a group which is capableof undergoing free radical polymerisation.

By way of example, the ligand may comprise one or more groups selectedfrom optionally substituted alkenyl groups, for example vinyl,vinylidene, allyl, butadienyl, isoprenyl, acrylate, methacrylate, vinylcarboxylates and vinyl ethers; aliphatic or aromatic thiols(thiophenols); and tin hydrides. Thus, where the polymerisable ligand isa ligand of the formula (1), at least one of R¹, R² and R³ may compriseone of these groups. Particularly preferred are ligands, for examplethose of Formula (1), which comprise one or more styryl, vinyl or allylgroups.

Of particular mention are phosphorus-based ligands of formula (1)including (4-styryl)diphenylphosphine, di-(4-styryl)phenylphosphine,tri-4-styrylphosphine, and corresponding 2-styryl and 3-styryl isomersthereof, (4-styryl)di-2-tolylphosphine, di-(4-styryl)-2-tolylphosphine,(4-styryl)di-2-tolylphosphine, di-(4-styryl)-2-tolylphosphine andcorresponding 2-styryl and 3-styryl isomers thereof,allyldiphenylphosphine, diallylphenylphosphine, triallylphosphine,allydibutylphosphine, vinyidiphenylphosphine, divinylphenylphosphine,trivinylphosphine, or one or the following ligands:

The polymerisable ligand may comprise a cyclopentadienyl group, whichmay be substituted or unsubstituted. For example, one or more of thering carbon atoms of the cyclopentadienyl group may be substituted witha group capable of binding to a polymeric structure. Of particularmention are cyclopentadienyl ligands of the following formulae:

-   -   wherein:        -   R⁴, R⁵, R⁶, R⁷ and R⁸ are each independently H or an            optionally substituted hydrocarbyl group, an optionally            substituted hydrocarbyloxy group, an optionally substituted            hydrocarbyl group where one or more carbon atoms in the            group are replaced by a sulphur, oxygen or nitrogen atom, or            an optionally substituted heterocyclyl group or two or more            of R⁴, R⁵, R⁶, R⁷ and R⁸ optionally being linked in such a            way as to form an optionally substituted ring(s); and        -   at least one of R⁴, R⁵, R⁶, R⁷ and R⁸ comprises a            polymerisable group.

Hydrocarbyl groups which may be represented by R⁴⁻⁸ independentlyinclude alkyl, alkenyl and aryl groups, and any combination thereof,such as aralkyl and alkaryl, for example benzyl groups.

Alkyl groups which may be represented by R⁴⁻⁸ include linear andbranched alkyl groups comprising up to 20 carbon atoms, particularlyfrom 1 to 7 carbon atoms and more particularly from 1 to 5 carbon atoms.When the alkyl groups are branched, the groups often comprise up to 10branch chain carbon atoms, in particular up to 4 branch chain atoms. Incertain embodiments, the alkyl group may be cyclic, commonly comprisingfrom 3 to 10 carbon atoms in the largest ring and optionally featuringone or more bridging rings. Examples of alkyl groups which may berepresented by R⁴⁻⁸ include methyl, ethyl, propyl, 2-propyl, butyl,2-butyl, t-butyl and cyclohexyl groups.

Alkenyl groups which may be represented by R⁴⁻⁸ include C₂₋₂₀, inparticular C₂₋₆ alkenyl groups. One or more carbon-carbon double bondsmay be present. The alkenyl group may carry one or more substituents,particularly phenyl substituents. Examples of alkenyl groups includevinyl, allyl, styryl and indenyl groups.

Aryl groups which may be represented by R⁴⁻⁸ may contain 1 ring or 2 ormore fused rings which may include cycloalkyl, aryl or heterocyclicrings. Examples of aryl groups which may be represented by R⁴⁻⁸ includephenyl, tolyl, fluorophenyl, pentafluorophenyl, chlorophenyl,bromophenyl, trifluoromethylphenyl, anisyl, naphthyl and ferrocenylgroups.

Heterocyclic groups which may be represented by R⁴⁻⁸ independentlyinclude aromatic, saturated and partially unsaturated ring systems andmay constitute 1 ring or 2 or more fused rings which may includecycloalkyl, aryl or heterocyclic rings. The heterocyclic group willcontain at least one heterocyclic ring, the largest of which willcommonly comprise from 3 to 7 ring atoms in which at least one atom iscarbon and at least one atom is any of N, O, S or P. Examples ofheterocyclic groups which may be represented by R⁴⁻⁸ include pyridyl,pyrimidyl, pyrrolyl, thiophenyl, furanyl, indolyl, quinolyl,isoquinolyl, imidazoyl and triazoyl groups.

Any of R⁴⁻⁸ may further comprise one or more other substituents. In thiscase, the one or more other substituents should normally be selected soas not to adversely affect the activity of the catalyst or the abilityof the group to undergo polymerisation. Examples of suitable optionalsubstituents include halogen, cyano, nitro, hydroxy, amino, thiol, acyl,hydrocarbyl, perhalogentated hydrocarbyl, heterocyclyl, hydrocarbyloxy,mono or di-hydrocarbylamino, hydrocarbylthio, esters, carboxylate,carbonates, amides, sulphonate, sulphonyl and sulphonamido groups,wherein the hydrocarbyl groups are as defined for R⁴⁻⁸ above.

Polymerisable cyclopentadienyl ligands may be incorporated into themicroencapsulated polymer in uncomplexed form (e.g. with 2 substituentsat the saturated carbon atom, one being a proton), or in the form of ametal complex of a cyclopentadienyl anion. Such complexes may beprepared using methods known to those skilled in the art, such asdeprotonation or reaction with a metal salt.

Of mention as polymerisable cyclopentadienyl ligands are those where oneor more of R⁴, R⁵, R⁶, R⁷ and R⁸ comprises a hydroxyalkyl, aminoalkyl oralkenyl group.

Of particular mention as polymerisable cyclopentadienyl ligands are1-(3-hydroxypropyl)-2,3,4,5-tetramethylcyclopentadiene,1-(4-hydroxybutyl)-2,3,4,5-tetramethylcyclopentadiene,1-(5-hydroxypentyl)-2,3,4,5-tetramethylcyclopentadiene,1-(3-aminopropyl)-2,3,4,5-tetramethylcyclopentadiene,1-(4-aminobutyl)-2,3,4,5-tetramethylcyclopentadiene,1-(5-aminopentyl)-2,3,4,5-tetramethylcyclopentadiene and1-(8-heptadecenyl)-2,3,4,5-tetramethylcyclopentadiene.

Polymerisation of the ligand may be performed using a free radicalpolymerisation process in which a ligand which is capable of undergoingfree radical polymerisation is contacted with a free radical initiator.“Free radical initiation” refers to any method of generating freeradicals.

Free radical polymerisation may be performed by any number of methodsknown to those skilled in the art. Examples of radical initiationmethods include thermal activation, where a functional group canspontaneously produce a free radical or a pair of free radicals solelyunder the influence of heat; photolytic activation, where a functionalgroup can spontaneously produce a free radical or a pair of freeradicals solely under the influence of electromagnetic radiation; andactivation using a chemical compound or a combination of chemicalcompounds which provide a free radical source upon applying certainconditions, for example heat or electromagnetic radiation. Usually achemical compound or a combination of chemical compounds which provide afree radical source upon applying certain conditions, for example heat(known as thermal initiators) or electromagnetic radiation (known asphotoinitiators), is employed as the free radical source.

Thermal activation can produce radicals from compounds with relativelyweak bonds such as vinyl-type polymerisable groups. It is known forexample that heating of pure styrene (i.e. containing no radicalinhibitors) produces free radicals by thermal homolytic cleavage of theπ-π bond, which then serve to initiate the polymerisation of thestyrene, eventually resulting in a gel.

Useful thermal initiators include azo, peroxide, persulfate, and redoxinitiators.

Suitable azo initiators include 2,2′-azobis(2,4-dimethylvaleronitrile)(VAZO™ 52); 2,2′-azobis(isobutyronitrile) (VAZO™ 64);2,2′-azobis-2-methylbutyronitrile (VAZO™ 67); and(1,1′-azobis(1-cyclohexanecarbonitrile) (VAZO™ 88), all of which areavailable from DuPont Chemicals, and 2,2′-azobis(methyl isobutyrate)(V-601) and 2,2′-azobis(2-amidinopropane)dihydrochloride (V-50™)available from Wako Chemicals. Also suitable is2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), formerly availablefrom DuPont Chemicals as VAZO™ 33.

Suitable peroxide initiators include diacyl peroxides,peroxydicarbonates, monoperoxycarbonates, peroxyketals, peroxyesters,dialkyl peroxides, hydroperoxides. Examples include benzoyl peroxide,acetyl peroxide, lauroyl peroxide, decanoyl peroxide, diacetylperoxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate (PERKADOX™16S, available from AKZO Chemicals), di(2-ethylhexyl) peroxydicarbonate,t-butyl peroxybenzoate, t-butyl peroxypivalate (LUPERSOL™ 1, availablefrom Atochem), t-butyl peroxy-2-ethylhexanoate (TRIGONOX™ 21-C50,available from Akzo Chemicals, Inc.), and dicumyl peroxide.

Suitable persulfate initiators include potassium persulfate, sodiumpersulfate, and ammonium persulfate.

Suitable redox (reduction-oxidation) initiators include combinations ofthe above persulfate initiators with reducing agents such as sodiummetabisulfite and sodium bisulfite; systems based on organic peroxidesand tertiary amines (for example, benzoyl peroxide plusdimethylaniline); and systems based on organic hydroperoxides orhydrogen peroxide and transition metals, for example, cumenehydroperoxide plus cobalt naphthenate.

Useful photoinitiators include those capable of being activated by UVradiation, e.g., at wavelengths from about 250 nm to about 450 nm, e.g.at about 351 nm. Useful photoinitiators include e.g. benzoin ethers suchas benzoin methyl ether and benzoin isopropyl ether, substituted benzoinethers, arylphospine oxide, substituted acetophenones such as2,2-dimethoxy-2-phenylacetophenone, and substituted alpha-ketols(alpha-hydroxyketones). Examples of commercially availablephotoinitiators include Irgacure™ 819 and Darocur™ 1173 (both availablefrom Ciba-Geigy Corp.), Lucern TPO™ (available from BASF) and Irgacure™651, (2,2-dimethoxy-1,2-diphenyl-1-ethanone, available from Ciba-Geigycorporation).

Of particular mention as free radical initiator systems are azocompounds and mixtures thereof.

A process of the present invention may be carried out using a freeradical initiator, which may be included in the composition of theencapsulation process. In this case, the free radical initiator ispreferably added to the organic phase of the encapsulation process. Thefree radical initiator may be used in a weight ratio to the ligandcomprising a functional group susceptible to attack by free radicalinitiation of between 10/1 and 1/10000, preferably between 1/2 and1/5000, more preferably between 1/10 and 1/2000 and highly preferablybetween 1/20 and 1/1000.

The ligand may be capable of copolymerising with the microcapsule shellor a constituent (e.g. a monomer or prepolymer) thereof. Suitablepolymerisation methods will be apparent to those skilled in the art. Forexample, in the case of a prepolymer comprising a polyisocyanate (e.g. adiisocyanate), a ligand which is capable of reacting with thepolyisocyanate can be contacted with the polyisocyanate, resulting in acomposition in which the ligand is covalently bound to the prepolymer.Subsequent polymerisation of the microcapsule material results in amicrocapsule comprising a ligand which is covalently bound to themicrocapsule shell. With regard to formula (1), at least one of R¹, R²and R³ may be capable of undergoing polymerisation with the microcapsulematerial.

By way of example, the ligand may comprise a group which is capable ofreacting with an isocyanate compound. Such groups include nucleophilicgroups, for example hydroxy, amino and mercapto groups. Thus, where thepolymerisable ligand is a ligand of the formula (1), at least one of R¹,R² and R³ may comprise one of these groups. An exemplary ligand is3-(diphenylphosphino)propyl-1-amine, i.e.:

Other compounds which are capable of reacting with isocyanate compoundsinclude active methylene compounds such as β-diketones, β-ketoesters,β-ketoamides, and β-dicarboxylic acids and derivatives thereof.Particular compounds include malonic acid and esters or amides thereof,malononitrile, cyanoacetic acid and esters or amides thereof, andacetoacetate compounds.

Exemplary processes involving copolymerisation of a ligand and apolyisocyanate are illustrated below:

In certain cases, it may be desirable to use a polymerisable ligandwhich is complexed with a metal, in particular the metal catalyst. Forexample, active methylene compounds such as β-diketones, β-ketoesters,β-ketoamides, and β-dicarboxylic acids and derivatives thereof may becomplexed with a transition metals (for example, Ni, Pd, Pt, Rh, Ru, Osor Ir), and the ligand subsequently polymerised with the microcapsulematerial. Of particular mention are transition metal (especially nickel)complexes formed with β-diketone ligands such astetramethylheptanedionate, acetoacetate and acetoacetonate ligands. Theuse of such complexes may provide a way of successfully encapsulatingnickel and other transition metal catalysts, which may otherwise provedifficult to encapsulate.

The ligand may comprise a plurality of moieties which are capable ofundergoing polymerisation. Thus, the ligand may be capable of undergoingfree radical polymerisation and may also bind with the microcapsuleshell or a constituent (e.g. a monomer or prepolymer) thereof. Forexample, a ligand may comprise a group which is capable of undergoingfree radical polymerisation (such as a vinyl group) and a groupcomprising an active methylene moiety (e.g. a group selected fromβ-diketones, β-ketoesters, β-ketoamides, β-dicarboxylic acid, aryl andheteroaryl groups). Examples of such ligands include acetoacetoxyethylmethacrylate, acetoacetoxyethyl acrylate, 2-vinylpyridine,4-vinylpyridine and 1-allylimidazole.

The ligand may comprise a plurality of groups which are capable ofpolymerising with the microcapsule shell or a constituent thereof,examples of such ligands including acetoacetoxyethyl ligands substitutedwith one or more of hydroxy, amino and mercapto; such ligands maypolymerise with the microcapsule material through either the keto or thehydroxy, amino or mercapto functionality. A particular ligand is2-acetoacetoxyethanol, i.e. CH₃C(O)CH₂C(O)OCH₂CH₂OH.

Catalyst

The catalyst may be an inorganic catalyst, in particular a transitionmetal catalyst. The term “transition metal catalyst” as used hereininclude reference to (a) the transition metal itself, normally in finelydivided or colloidal form; (b) a complex of a transition metal; or (c) acompound containing a transition metal. If desired a pre-cursor for thecatalyst may be microencapsulated within the polymer microcapsule shelland subsequently converted to the catalyst, for example by heating. Theterm “catalyst” as used herein thus also includes a catalyst pre-cursor.

Transition metals on which a catalyst for use in the invention is basedmay include platinum, palladium, osmium, ruthenium, rhodium, iridium;rhenium, scandium, cerium, samarium, yttrium, ytterbium, lutetium,cobalt, titanium, chromium, copper, iron, nickel, manganese, tin,mercury, silver, gold, zinc, vanadium, tungsten and molybdenum.Particular catalysts for use in the present invention may be basedinclude osmium, ruthenium, rhodium, platinum, titanium, nickel, vanadiumand chromium, and especially palladium. Air sensitive catalysts may behandled using conventional techniques to exclude air.

Palladium in a variety of forms may be microencapsulated according tothe present invention and is useful as a catalyst for a wide range ofreactions.

Preferably palladium is used directly in the form of an organic solventsoluble form and is more preferably palladium acetate. Thus for examplepalladium acetate may be suspended or more preferably dissolved in asuitable solvent such as a hydrocarbon solvent or a chlorinatedhydrocarbon solvent and the resultant solution may be microencapsulatedaccording to the present invention. Chloroform is a preferred solventfor use in the microencapsulation of palladium acetate.

According to literature sources palladium acetate decomposes to themetal under the action of heat. Catalysts of the present inventionderived from palladium acetate have proved to be effective, although itis not presently known whether palladium is present in the form of themetal or remains as palladium acetate.

It is understood that one or more ligands and/or one or more catalystsmay be employed in the process of the present invention. Where multipleligands and/or multiple catalysts are employed, each independently maybe selected for the ability to enhance or catalyse the same or similarreaction types, or for the ability to enhance or catalyse differentreaction types.

Microcapsule Preparation

A microencapsulated catalyst-ligand system of the invention is usuallyprepared by an interfacial polymerisation process. Interfacialpolymerisation processes are described in, for example, WO 03/006151.

There are various types of interfacial polymerisation techniques but allinvolve reaction at the interface of a dispersed phase and a continuousphase in an emulsion system. Typically the dispersed phase is an oilphase and the continuous phase is an aqueous phase but interfacialpolymerisation reactions at the interface of a continuous oil phase anda dispersed aqueous phase are also possible. Thus for example an oil ororganic phase is dispersed into a continuous aqueous phase comprisingwater and a surface-active agent. The organic phase is dispersed asdiscrete droplets throughout the aqueous phase by means ofemulsification, with an interface between the discrete organic phasedroplets and the surrounding continuous aqueous phase solution beingformed. Polymerisation at this interface forms the microcapsule shellsurrounding the dispersed phase droplets.

In one type of interfacial condensation polymerisationmicroencapsulation process, monomers contained in the oil and aqueousphase respectively are brought together at the oil/water interface wherethey react by condensation to form the microcapsule wall. In anothertype of polymerisation reaction, the in situ interfacial condensationpolymerisation reaction, all of the wall-forming monomers are containedin the oil phase. In situ condensation of the wall-forming materials andcuring of the polymers at the organic-aqueous phase interface may beinitiated by heating the emulsion to a temperature of between about 20°C. to about 100° C. and optionally adjusting the pH. The heating occursfor a sufficient period of time to allow substantial completion of insitu condensation of the prepolymers to convert the organic droplets tocapsules consisting of solid permeable polymer shells entrapping theorganic core materials.

One type of microcapsule prepared by in situ condensation and known inthe art is exemplified in U.S. Pat. Nos. 4,956,129 and 5,332,584. Thesemicrocapsules, commonly termed “aminoplast” microcapsules, are preparedby the self-condensation and/or cross-linking of etherifiedurea-formaldehyde resins or prepolymers in which from about 50 to about98% of the methylol groups have been etherified with a C₄-C₁₀ alcohol(preferably n-butanol). The prepolymer is added to or included in theorganic phase of an oil/water emulsion. Self-condensation of theprepolymer takes place optionally under the action of heat at low pH. Toform the microcapsules, the temperature of the two-phase emulsion israised to a value of from about 20° C. to about 90° C., preferably fromabout 40° C. to about 90° C., most preferably from about 40° C. to about60° C. Depending on the system, the pH value may be adjusted to anappropriate level. For the purpose of this invention a pH of about 1.5to 3 is appropriate:

As described in U.S. Pat. No. 4,285,720 the prepolymers most suitablefor use in this invention are partially etherified urea-formaldehydeprepolymers with a high degree of solubility in organic phase and a lowsolubility in water. Etherifed urea-formaldehyde prepolymers arecommercially available in alcohol or in a mixture of alcohol and xylene.Examples of preferred commercially available prepolymers include theBeetle etherified urea resins manufactured by BIP (e.g. BE607, BE610,BE660, BE676) or the Dynomin N-butylated urea resins from Dyno Cyanamid(e.g. Dynomin UB-24-BX, UB-90-BX etc.).

Acid polymerisation catalysts capable of enhancing the microcapsuleformation can be placed in either the aqueous or the organic phase. Acidpolymerisation catalysts are generally used when the core material istoo hydrophobic, since they serve to attract protons towards the organicphase. Any water soluble acid polymerisation catalyst which has a highaffinity for the organic phase can be used. Carboxylic and sulphonicacids are particularly useful.

One further type of microcapsule prepared by in situ condensation andfound in the art, as exemplified in U.S. Pat. No. 4,285,720 is apolyurea microcapsule which involves the use of at least onepolyisocyanate such as polymethylene polyphenyleneisocyanate (PMPPI)and/or tolylene diisocyanate (TDI) as the wall-forming material. In thecreation of polyurea microcapsules, the wall-forming reaction isgenerally initiated by heating the emulsion to an elevated temperatureat which point a proportion of the isocyanate groups are hydrolyzed atthe interface to form amines, which in turn react with unhydrolyzedisocyanate groups to form the polyurea microcapsule wall. During thehydrolysis of the isocyanate monomer, carbon dioxide is liberated. Theaddition of no other reactant is required once the dispersionestablishing droplets of the organic phase within a continuous liquidphase, i.e., aqueous phase, has been accomplished. Thereafter, andpreferably with moderate agitation of the dispersion, the formation ofthe polyurea microcapsule can be brought about by heating the continuousliquid phase or by introducing a polymerisation catalyst such as analkyl tin or a tertiary amine capable of increasing the rate ofisocyanate hydrolysis.

The amount of the organic phase may vary from about 1% to about 75% byvolume of the aqueous phase present in the reaction vessel. A preferredamount of organic phase is about 10 percent to about 50 percent byvolume. The organic polyisocyanates used in this process includes botharomatic and aliphatic mono and poly functional isocyanates. Examples ofsuitable aromatic diisocyantes and other polyisocyantes include thefollowing: 1-chloro-2,4-phenylene diisocyante, m-phenylene diisocyante(and its hydrogenated derivative), p-phenylene diisocyante (and itshydrogenated derivative), 4,4′-methylenebis (phenyl isocyanate),2,4-tolylene diisocyanate, tolylene diisocyanate (60% 2,4-isomer, 40%2,6-isomer), 2,6-tolylene diisocyante, 3,3′-dimethyl-4,4′-biphenylenediisocyante, 4,4′-methylenebis (2-methylphenyl isocyanate),3,3′-dimethoxy-4,4′-biphenylene diisocyanate,2,2′,5,5′-tetramethyl-4,4′-biphenylene diisocyanate, 80% 2,4- and 20%2,6-isomer of tolylene diisocyanate, polymethylene polyphenylisocyante(PMPPI), 1,6-hexamethylene diisocyanate, isophorone diisocyanate,tetramethylxylene diisocyanate and 1,5-naphthylene diisocyanate,hydrophilic aliphatic polyisocyanates based on hexamethylenediisocyanate (e.g. Bayhydur 3100, Bayhydur VP LS2319 and Bayhydur VPLS2336) and hydrophilic aliphatic polyisocyanates based on isophoronediisocyanate (e.g. Bayhydur VP LS2150/1)

It may be desirable to use combinations of the above mentionedpolyisocyantes. Particular polyisocyantes are polymethylenepolyphenylisocyante (PMPPI) and mixtures of polymethylenepolyphenylisocyante (PMPPI) with tolylene diisocyanate or otherdifunctional aromatic or aliphatic isocyantes.

One further class of polymer precursors consists of a primarilyoil-soluble component and a primarily water-soluble component whichreact together to undergo interfacial polymerisation at a water/oilinterface. Typical of such precursors are an oil-soluble isocyanate suchas those listed above and a water-soluble poly amine such asethylenediamine and/or diethylenetriamine to ensure that chain extensionand/or cross-linking takes place. Cross-linking variation may beachieved by increasing the functionality of the amine. Thus for example,cross-linking is increased if ethylenediamine is replaced by apolyfunctional amine such as DETA (diethylene triamine), TEPA(tetraethylene pentamine) and other well established cross linkingamines. Isocyanate functionality can be altered (and thus cross-linkingalso altered) by moving from monomeric isocyanates such as toluenediisocyanate to PMPPI. Mixtures of isocyanates, for example mixtures oftolylene diisocyanate and PMPPI, may also be used. Moreover, thechemistry may be varied from aromatic isocyanates to aliphaticisocyanates such as hexamethylenediisocyanate and isophoronediisocyanate. Further modifications can be achieved by partiallyreacting the (poly) isocyanate with a polyol to produce an amount of apolyurethane within the isocyanate chemistry to induce differentproperties to the wall chemistry. For example, suitable polyols couldinclude simple low molecular weight aliphatic di, tri or tetraols orpolymeric polyols. The polymeric polyols may be members of any class ofpolymeric polyols, for example: polyether, polyTHF, polycarbonates,polyesters and polyesteramides. One skilled in the art will be aware ofmany other chemistries available for the production of a polymeric wallabout an emulsion droplet. As well as the established isocyanate/aminereaction to produce a polyurea wall chemistry, there can be employedimprovements to this technology including for example that in whichhydrolysis of the isocyanate is allowed to occur to an amine which canthen further react internally to produce the polyurea chemistry (asdescribed for example in U.S. Pat. No. 4,285,720). Variation in thedegree of cross-linking may be achieved by altering the ratio ofmonomeric isocyanate to polymeric isocyanate. As with the conventionalisocyanate technology described above, any alternative isocyanates canbe employed in this embodiment.

One skilled in the art will be aware that the various methods previouslydescribed to produce polyurea microcapsules typically leave unreactedamine (normally aromatic amine) groups attached to the polymer matrix.In some cases it may be advantageous to convert such amine groups to asubstantially inert functionality. Preferred are methods for theconversion of such amine groups to urea, amide or urethane groups bypost reaction of the microcapsules in an organic solvent with amonoisocyanate, acid chloride or chloroformate respectively.

U.S. Pat. No. 6,020,066 (assigned to Bayer AG) discloses another processfor forming microcapsules having walls of polyureas and polyiminoureas,wherein the walls are characterized in that they consist of reactionproducts of crosslinking agents containing NH₂ groups with isocyanates.The crosslinking agents necessary for wall formation include di- orpolyamines, diols, polyols, polyfunctional amino alcohols, guanidine,guanidine salts, and compounds derived therefrom. These agents arecapable of reacting with the isocyanate groups at the phase interface inorder to form the wall.

Preferred materials for the microcapsule include a polyurea, formed asdescribed in U.S. Pat. No. 4,285,720 or a urea-formaldehyde polymer asdescribed in U.S. Pat. No. 4,956,129. Polyurea is preferred because themicrocapsule is formed under very mild conditions and does not requireacidic pH to promote polymerisation and so is suitable for use whenencapsulating acid-sensitive catalysts. The most preferred polymer typefor the microcapsule is polyurea as described in U.S. Pat. No. 4,285,720based on the PMPPI polyisocyanate either alone or in combination withother aromatic di or multi functional isocyantes.

Microencapsulation techniques described above most commonly involve themicroencapsulation of an oil phase dispersed within an aqueouscontinuous phase, and for such systems the catalyst is suitably capableof being suspended within the microencapsulated oil phase or morepreferably is soluble in a water-immiscible organic solvent suitable foruse as the dispersed phase in microencapsulation techniques. The scopeof the present invention is not however restricted to the use ofoil-in-water microencapsulation systems and water-soluble catalysts maybe encapsulated via interfacial microencapsulation of water-in-oilemulsion systems. Water-soluble catalysts may also be encapsulated viainterfacial microencapsulation of water-in-oil-in-water emulsionsystems.

The microcapsule wall-forming material may for example be a monomer,oligomer or pre-polymer and polymerisation of the material may takeplace in situ by polymerisation and/or curing of the wall-formingmaterial at the interface. As an alternative, polymerisation may takeplace at the interface by the bringing together of a first wall-formingmaterial added through the continuous phase and a second wall-formingmaterial in the discontinuous phase.

The ligand may be encapsulated along with the metal catalyst as acomponent of the organic phase. Thus, the ligand, metal catalyst,solvent, wall forming material and one or more optional other components(such as a free radical initiator) may be dispersed as a single organicphase into the continuous aqueous phase. However, if any of thecomponents are incompatible with one another, it may be advantageous todisperse all the components separately or in combinations wherein thecontinuous phase conditions are such that the microcapsulepolymerisation is delayed until the separate organic components havemixed through diffusion and particle coalescence and division. Forexample, the ligand can be dissolved in an organic solvent and thendispersed into the aqueous phase either simultaneously with the otherorganic components or after dispersion of the organic solution of themetal catalyst, wall forming material and optional components (e.g. afree radical initiator). In particular, an organic-soluble ligand may bedissolved along with the metal catalyst, the polymerisable wall formingreactants any optional components (e.g. a free radical initiator), whichare then dispersed as a single solution into the continuous aqueousphase. The ligand may be polymerised prior to, during or after formationof the microcapsule shell. The ligand may self-polymerise or maycopolymerise with the microcapsule shell or a constituent (e.g. amonomer or prepolymer) thereof.

A process of the invention may therefore comprise:

-   -   (a) dissolving or dispersing the catalyst and ligand in a first        phase,    -   (b) dispersing the first phase in a second, continuous phase to        form an emulsion,    -   (c) reacting one or more microcapsule wall-forming materials at        the interface between the dispersed first phase and the        continuous second phase to form a microcapsule polymer shell        encapsulating the dispersed first phase core, and optionally    -   (d) recovering the microcapsules from the continuous phase.

Preferably, the first phase is an organic phase and the second,continuous phase is an aqueous phase. Suitably a protective colloid(surfactant) is used to stabilise the emulsion. If desired the recoveredmicrocapsules may be washed with a suitable solvent to extract the firstphase, and in particular the organic phase solvent from the core and anyloosely bound metal catalyst or ligand. A suitable solvent, usuallywater, may also be used to remove the protective colloid or surfactant.As mentioned above, the ligand may be polymerised prior to, during orafter formation of the microcapsule shell. The ligand mayself-polymerise or may copolymerise with the microcapsule shell or aconstituent (e.g. a monomer or prepolymer) thereof.

In some circumstances, particularly where the ligand is highly reactiveor may interfere with the interfacial polymerisation process, it may beadvantageous to introduce the ligand after the interfacialpolymerisation. The microcapsule shell may, therefore, be formed byinterfacial polymerisation in the presence of a catalyst and treatedwith the ligand. The microencapsulated catalyst may be isolated beforesubsequent treatment with the ligand. Treatment with the ligand may becarried with or without the need to swell the permeable polymermicrocapsule shell. The ligand may self-polymerise or may copolymerisewith the microcapsule shell or a constituent (e.g. a monomer orprepolymer) thereof. Typically, the microcapsules are treated with apolymerisable ligand, which is subsequently polymerised.

A process of the invention may therefore comprise:

-   -   (a) dissolving or dispersing the catalyst in a first phase,    -   (b) dispersing the first phase in a second, continuous phase to        form an emulsion,    -   (c) reacting one or more microcapsule wall-forming materials at        the interface between the dispersed first phase and the        continuous second phase to form a microcapsule polymer shell        encapsulating the dispersed first phase core, and    -   (d) treating the microcapsules with the ligand.

The microcapsules may be recovered from the continuous phase in step (c)before treating with the ligand in step (d). The ligand-treatedmicrocapsules may be isolated and washed with solvent. The ligand mayself-polymerise or may copolymerise with the microcapsule shell or aconstituent (e.g. a monomer or prepolymer) thereof. Typically, themicrocapsules are treated with a polymerisable ligand, which issubsequently polymerised.

In some circumstances, particularly where the metal catalyst is highlyreactive or may interfere with the interfacial polymerisation process,it may be advantageous to introduce the metal catalyst after formationof the microcapsule. A process of the invention may therefore compriseforming a microcapsule shell by interfacial polymerisation in thepresence of a ligand and then treating the microcapsule shell with acatalyst solution. The microencapsulated ligand may be isolated prior totreatment with the catalyst. Treatment with the metal catalyst may becarried with or without the need to swell the permeable polymermicrocapsule shell. The ligand may be polymerised prior to, during orafter formation of the microcapsule shell. Typically, the ligand ispolymerised prior to treatment with the catalyst solution, e.g. prior orduring formation of the microcapsule shell. The ligand mayself-polymerise or may copolymerise with the microcapsule shell or aconstituent (e.g. a monomer or prepolymer) thereof.

A process of the invention may therefore comprise:

-   -   (a) dissolving or dispersing the ligand in a first phase,    -   (b) dispersing the first phase in a second, continuous phase to        form an emulsion,    -   (c) reacting one or more microcapsule wall-forming materials at        the interface between the dispersed first phase and the        continuous second phase to form a microcapsule polymer shell        encapsulating the dispersed first phase core, and    -   (d) treating the microcapsules with a solution of a catalyst.

The microcapsules may be recovered from the continuous phase in step (c)before treating with the catalyst in step (d). The catalyst-treatedmicrocapsules may be isolated and washed with solvent. As mentionedabove, the ligand may be polymerised prior to, during or after formationof the microcapsule shell. Typically, the ligand is polymerised prior totreatment with the catalyst solution. The ligand may self-polymerise ormay copolymerise with the microcapsule shell or a constituent (e.g. amonomer or prepolymer) thereof.

With regard to the above processes, of particular mention are those inwhich the polymerisable ligand is encapsulated along with the metalcatalyst as a component of the organic phase. Also of mention areprocesses in which the polymerisable ligand is first encapsulated as acomponent of the organic phase and then the metal catalyst post-adsorbedinto the encapsulated polymeric ligand by exposing the entrapped ligandto a solution of the metal catalyst. Also of mention are processes inwhich the polymerisable ligand is post-adsorbed into themicroencapsulated metal catalyst by exposing the entrapped metal to anorganic solution of the ligand.

The molar ratio of ligand to metal catalyst may be in the range of 1/100to 100/1, more preferably in the range of 1/20 to 20/1, and morepreferably in the range of 1/10 to 10/1.

Preferred ligands include those soluble in organic solvents and notsensitive to water.

Preferably, the continuous phase is water. The amount of organic phasedispersed into the aqueous phase may vary from 1% to about 75% by volumeof the aqueous phase present in the reactor. Preferably the amount oforganic phase is about 10% to about 50% by volume.

The weight % wall forming material in the organic phase (which mayinclude one or more of the ligand, catalyst and solvent) is in the range5 to 95%, more preferably 10 to 70% and most preferably 10 to 50%.

The weight % of solvent in the organic phase (which may include one ormore of the ligand, catalyst and wall-forming material) is in the range5 to 95%, more preferably 15 to 90% and most preferably 40 to 80%.

The loading level of the microencapsulated catalyst can be varied.Microencapsulated catalysts with loadings 0.01 mmol/g to 0.8 mmol/g aretypical, especially where the loading is based on metal content.Loadings of 0.05 mmol/g to 0.6 mmol/g are preferred.

The microencapsulation of the catalyst and ligand takes place accordingto techniques well known in the art. Typically the catalyst is dissolvedor dispersed in an oil phase which is emulsified into a continuousaqueous phase to form an emulsion which is generally stabilised by asuitable surfactant system. A wide variety of surfactants suitable forforming and stabilising such emulsions are commercially available andmay be used either as the sole surfactant or in combination. Theemulsion may be formed by conventional low or high-shear mixers orhomogenisation systems, depending on particle size requirements. A widerange of continuous mixing techniques can also be utilised. Suitablemixers which may be employed in particular include dynamic mixers whosemixing elements contain movable parts and static mixers which utilisemixing elements without moving parts in the interior. Combinations ofmixers (typically in series) may be advantageous. Examples of the typesof mixer which may be employed are discussed in U.S. Pat. No. 627,132which is herein incorporated by reference. Alternatively, emulsions maybe formed by membrane emulsification methods. Examples of membraneemulsification methods are reviewed in Journal of Membrane Science 169(2000) 107-117 which is herein incorporated by reference.

Typical examples of suitable surfactants include:

-   -   a) condensates of alkyl (eg octyl, nonyl or polyaryl)phenols        with ethylene oxide and optionally propylene oxide and anionic        derivatives thereof such as the corresponding ether sulphates,        ether carboxylates and phosphate esters;    -   b) block copolymers of polyethylene oxide and polypropylene        oxide such as the series of surfactants commercially available        under the trademark PLURONIC (PLURONIC is a trademark of BASF);    -   c) TWEEN surfactants, a series of emulsifiers comprising a range        of sorbitan esters condensed with various molar proportions of        ethylene oxide;    -   d) condensates of C₈ to C₃₀ alkanols with from 2 to 80 molar        proportions of ethylene oxide and optionally propylene oxide;        and    -   e) polyvinyl alcohols, including the carboxylated and        sulphonated products.

Furthermore, WO 01/94001 teaches that one or more wall modifyingcompounds (termed surface modifying agents) can, by virtue of reactionwith the wall forming materials, be incorporated into the microcapsulewall to create a modified microcapsule surface with built in surfactantand/or colloid stabiliser properties. Use of such modifying compoundsmay enable the organic phase wall forming material to be more readilydispersed into the aqueous phase possibly without the use of additionalcolloid stabilisers or surfactants and/or with reduced agitation. Theteaching of WO 01/94001 is herein incorporated by reference. Examples ofwall modifying compounds which may find particular use in the presentinvention include anionic groups such as sulphonate or carboxylate,non-ionic groups such as polyethylene oxide or cationic groups such asquaternary ammonium salts.

In addition the aqueous phase may contain other additives which may actas aids to the process of dispersion or the reaction process. Forexample, de-foamers may be added to lesson foam build up, especiallyfoaming due to gas evolution.

A wide variety of materials suitable for use as the oil phase will occurto one skilled in the art. Examples include, diesel oil, isoparaffin,aromatic solvents, particularly alkyl substituted benzenes such asxylene or propyl benzene fractions, and mixed napthalene and alkylnapthalene fractions; mineral oils, white oil, castor oil, sunfloweroil, kerosene, dialkyl amides of fatty acids, particularly the dimethylamides of fatty acids such as caprylic acid; chlorinated aliphatic andaromatic hydrocarbons such as 1,1,1-trichloroethane and chlorobenzene,esters of glycol derivatives, such as the acetate of the n-butyl, ethyl,or methyl ether of diethylene glycol, the acetate of the methyl ether ofdipropylene glycol, ketones such as isophorone andtrimethylcyclohexanone (dihydroisophorone) and the acetate products suchas hexyl, or heptyl acetate. Organic liquids conventionally preferredfor use in microencapsulation processes are xylene, diesel oil,isoparaffins and alkyl substituted benzenes, although some variation inthe solvent may be desirable to achieve sufficient solubility of thecatalyst in the oil phase.

Certain catalysts may catalyse the wall-forming reaction duringinterfacial polymerisation. In general it is possible to modify themicroencapsulation conditions to take account of this. Some interaction,complexing or bonding between the catalyst and the polymer shell may bepositively desirable since it may prevent agglomeration of finelydivided or colloidal catalysts.

In some instances, the catalyst and/or ligand being encapsulated mayincrease the rate of the interfacial polymerisation reactions. In suchcases it may be advantageous to cool one or both of the organic andcontinuous aqueous phases such that interfacial polymerisation islargely prevented whilst the organic phase is being dispersed. Thereaction is then initiated by warming in a controlled manner once therequired organic droplet size has been achieved. For example, in certainreactions the aqueous phase may be cooled to less than 10° C., typicallyto between 0° C. to 10° C., prior to addition of the oil phase and thenwhen the organic phase is dispersed the aqueous phase may be heated toraise the temperature above 15° C. to initiate polymerisation.

Microencapsulation of the oil phase droplets containing the catalyst andthe ligand may take place by an interfacial polymerisation reaction asdescribed above under an inert atmosphere. The aqueous dispersion ofmicrocapsules containing the catalyst and ligand may be used to catalysea suitable reaction without further treatment. Preferably however themicrocapsules containing the catalyst and the ligand are removed fromthe aqueous phase by filtration. It is especially preferred that therecovered microcapsules are washed with water to remove any remainingsurfactant system and with a solvent capable of extracting the organicphase contained within the microcapsule. Relatively volatile solventssuch as halogenated hydrocarbon solvents for example chloroform aregenerally more readily removed by washing or under reduced pressure thanare conventional microencapsulation solvents such as alky substitutedbenzenes. If the majority of the solvent is removed, the resultantmicrocapsule may in effect be a substantially solvent-free polymer beadcontaining the catalyst efficiently dispersed within the microcapsulepolymer shell. The process of extracting the organic phase may cause themicrocapsule walls to collapse inward, although the generally sphericalshape will be retained. If desired the dry microcapsules may be screenedto remove fines, for example particles having a diameter less than about20 microns.

In the case of the microencapsulated palladium acetate microparticles,it is preferred that the recovered water wet microcapsules are washedwith copious quantities of deionised water, followed by sequentialN,N-dimethylformamide, ethanol, toluene washes and finally hexane orheptane washes. The microcapsules are then dried in a vac oven at 50° C.for approx 4 hours to give a product with greater than 95% non volatilecontent (by exhaustive drying) and preferably greater than 98% nonvolatile content.

Use

Depending on the conditions of preparation and in particular the degreeof interaction between the catalyst, the ligand and the wall-formingmaterials, the microencapsulated catalyst-ligand system of the presentinvention may be regarded at one extreme as a ‘reservoir’ in which thefinely divided catalyst and ligand (either as solid or in the presenceof residual solvent) is contained within an inner cavity bound by anintegral outer polymer shell or at the other extreme as a solid,amorphous polymeric bead throughout which the finely divided catalystand ligand is distributed. In practice the position is likely to bebetween the two extremes. Regardless of the physical form of theencapsulated catalyst-ligand of the present invention and regardless ofthe exact mechanism by which access of reactants to the catalyst takesplace (diffusion through a permeable polymer shell or absorption into aporous polymeric bead), it has been found that encapsulated catalystsand ligands of the present invention permit effective access of thereactants to the catalyst whilst presenting the catalyst and ligand in aform in which it can be recovered and if desired re-used. Furthermore,since in a preferred embodiment the polymer shell/bead is formed in situby controlled interfacial polymerisation (as opposed to uncontrolleddeposition from an organic solution of the polymer), a microencapsulatedcatalyst-ligand system of the present invention may be used in a widerange of organic solvent-based reactions.

The microcapsules of this invention are regarded as being insoluble inmost common organic solvents by virtue of the fact that they are highlycross-linked. As a consequence, the microcapsules can be used in a widerange of organic solvent-based reactions.

The microcapsules may be added to the reaction system to be catalysedand, following completion of the reaction, may be recovered for exampleby filtration. The recovered microcapsules may be returned to catalyse afurther reaction and re-cycled as desired. Alternatively, themicrocapsules containing the catalyst and ligand may be used as astationary catalyst in a continuous reaction. For instance, themicrocapsule particles could be immobilised with a porous support matrix(e.g. a membrane). The microcapsules are permeable to the extent thatcatalysis may take place either by diffusion of the reaction mediumthrough the polymer shell walls or by absorption of the reaction mediumthrough the pore structure of the microcapsule.

The following Examples illustrate the present invention.

Example 1

Various types of microencapsulated palladium acetate-ligand systems wereproduced. The systems were then used in a Suzuki-type reaction and thepalladium content of the crude product determined.

In Systems 1A and 1B, palladium acetate was coencapsulated with ap-styryldiphenylphosphine ligand. System 1C was a similar system exceptthat it contained a triphenylphosphine ligand.

In System 2, palladium acetate was coencapsulated with atriphenylphosphine ligand.

Systems 3A and 3B were obtained using a process of the presentinvention. Palladium acetate was encapsulated withp-styryldiphenylphosphine ligand and the ligand polymerised using a freeradical polymerisation process.

In the following procedures, GOSHENOL is polyvinyl alcohol; SOLVESSO 200is a high boiling (230-257° C.) mixture of aromatics (mainlynaphthalenes); TERGITOL XD is the polyoxypropylene polyoxyethylene etherof butyl alcohol; and REAX 100M is sodium lignosulfonate. REAX, TERGITOLand GOSHENOL are added as colloid stabilisers and detergents.

Preparation of Systems 1A, 1B and 1C

An organic phase was formed from palladium(II) acetate (Pd(OAc)₂)dissolved in chloroform, and then stirred for 10 minutes followed byaddition of p-styryidiphenylphosphine or triphenylphosphine ligand, andthen stirred for a further 30 minutes. To this mixture was addedpolymethylene polyphenylene di-isocyanate (PMPPI) and the contentsstirred for a further 60 minutes.

An aqueous phase was made up consisting of 40% aqueous REAX 100 Msolution, 20% aqueous TERGITOL XD solution and 25% aqueous poly(vinylalcohol) (PVOH) (Gohsenol GLO3) solution in deionised water and chargedto a Radley's Carousel tube on a Radley's Cooled Carousel unit.

The organic phase mixture was then added via a syringe over ca. 30seconds to the aqueous phase and held at 1° C. while shearing (using across-shaped magnetic stirrer) with the stirrer setting on thestirrer-hotplate at 8. The reaction was maintained under inertatmosphere (N₂) throughout. After 3 minutes, the stirrer setting wasreduced to 6 and a few drops of de-foamer (DrewPLus S4382) were addedduring the onset of polymerisation (detected by carbon dioxideevolution). The suspension thus obtained was warmed to room temperatureover 1 hour and stirred for a further 18 hours. The Carousel tube wasthen transferred to a heated Carousel unit and heated at 65° C. for afurther 2 hours. The resulting microcapsules were then filtered though apolyethylene frit (20 micron porosity) and washed on a filter bedaccording to the following sequence: deionised water (5×10 ml), DMF(2×10 ml), ethanol (3×10 ml), toluene (2×10 ml) and hexane (2×10 ml),and finally dried in a vacuum oven at 45° C.

The loading properties of Systems 1A, 1B and 1C are given in Table 1,together with the quantities and ratios of reagents used in theirpreparation.

TABLE 1 System System System 1A 1B 1C Oil phase: CHCl₃ (g) 2.40 2.402.40 PMPPI (g) 1.20 1.20 1.20 Pd(OAc)₂ (g) 0.20 0.22 0.20p-Styryldiphenylphosphine (g) 0.13 0.28 — Triphenylphosphine (g) — —0.12 Aqueous Phase: DI water (g) 4.95 5.17 4.94 40% Reax 100M Soln (g)0.59 0.62 0.59 25% PVOH soln (g) 0.47 0.49 0.47 20% Tergitol soln (g)0.29 0.31 0.29 Target Properties: Pd/P ratio 1:0.5 1:1 1:0.5 Targetloading of Pd(OAc)₂ 0.58 0.58 0.59 (mmol/g) Target loading of ligand0.29 0.57 0.30 (mmol/g)

Preparation of System 2

An organic phase was formed under nitrogen from Pd(OAc)₂ (2.00 g, 98%)dissolved in chloroform (44.7 g), and then stirred for 10 minutesfollowed by addition of triphenylphosphine (2.40 g, 1:1 Pd/P molarratio), and then stirred for a further 30 minutes. To this mixture,polymethylene polyphenylene di-isocyanate (PMPPI) (17.60 g) was addedand the contents stirred for a further 60 minutes.

An aqueous phase was made up containing 40% REAX 100 M solution (13.34g), 20% TERGITOL XD solution (6.67 g) and 25% poly (vinyl alcohol)(PVOH) solution (10.67 g) in deionised water (112 g).

The organic phase mixture was then added to an aqueous phase and held at1° C. while shearing (using a FISHER 4-blade retreat-curve stirrer) at425 rpm for 8 minutes. The reaction was maintained under inertatmosphere (N₂) throughout. After 8 minutes the shear rate was reducedto 225 rpm and few drops of de-foamer (DrewPLus S4382) were added duringthe onset of polymerisation (detected by carbon dioxide evolution). Thesuspension thus obtained was warmed to 12° C. and stirred for a further16 hours, then at 40° C. for 5 hours. The resulting microcapsules werethen filtered though a polyethylene frit (20 micron porosity) and washedon a filter bed according to the following sequence: deionised water(5×100 ml), ethanol (3×100 ml), hexane (3×100 ml), and finally dried ina vacuum oven at 50° C.

ICP Analysis: 4.0% Pd wt/wt, Loading: 0.38 mmol/g (95% Pd encapsulated)

-   -   1.2% P wt/wt, Loading: 0.39 mmol/g (93% P encapsulated)

Preparation of Systems 3A and 3B

The organic phase was formed from palladium(II) acetate (Pd(OAc)₂)dissolved in chloroform and then stirred for 10 minutes followed byaddition of p-styryldiphenylphosphine and then stirred for a further 30minutes. To this mixture was added polymethylene polyphenylenedi-isocyanate (PMPPI) and 2,2′-azobisisobutyronitrile (AIBN) and thecontents stirred for a further 60 minutes.

An aqueous phase was made up consisting of 40% aqueous REAX 100 Msolution, 20% aqueous TERGITOL XD solution and 25% aqueous poly(vinylalcohol) (PVOH) (Gohsenol GLO3) solution in deionised water and chargedto a Radley's Carousel tube on a Radley's Cooled Carousel unit.

The organic phase mixture was then added via a syringe over ca 30seconds to the aqueous phase held at 1° C. while shearing (using across-shaped magnetic stirrer) with stirrer setting on thestirrer-hotplate at 8. The reaction was maintained under inertatmosphere (N₂) throughout. After 3 minutes the stirrer setting wasreduced to 6 and a few drops of de-foamer (DrewPLus S4382) were addedduring the onset of polymerisation (detected by carbon dioxideevolution). The suspension thus obtained was warmed to room temperatureover 1 hour and stirred for a further 18 hours. The Carousel tube wasthen transferred to a heated Carousel unit and heated at 65° C. for afurther 2 hours. The resulting microcapsules were then filtered though apolyethylene frit (20 micron porosity) and washed on a filter bedaccording to the following sequence: deionised water (5×10 ml), DMF(2×10 ml), ethanol (3×10 ml), toluene (2×10 ml) and hexane (2×10 ml),and finally dried in a vacuum oven at 45° C.

The loading properties of Systems 3A and 3B are given in Table 2,together with the quantities and ratios of reagents used in theirpreparation.

TABLE 2 System System 3A 3B Oil phase: CHCl₃ (g) 2.40 2.40 PMPPI (g)1.20 1.20 Pd(OAc)₂ (g) 0.20 0.22 AIBN (g) 0.001 0.003(p-Styryldiphenyl)phosphine 0.13 0.28 Ligand (g) Aqueous Phase: DI water(g) 4.95 5.17 40% Reax 100M Soln (g) 0.59 0.62 25% PVOH soln (g) 0.470.49 20% Tergitol soln (g) 0.29 0.31 Target Properties: Pd:P mol ratio1:0.5 1:1 Target loading Pd(OAc)2 0.58 0.58 mmol/g Target loading Ligandmmol/g 0.29 0.57 Achieved Properties: (ICP Analysis) Loading Pd (mmol/g)0.48 0.50 Loading P (mmol/g) 0.29 0.45

General Procedure for Suzuki-Type Reaction

Each System was reacted with 4-methoxyphenylboronic acid and4-bromofluorobenzene in a Suzuki-type reaction, and the palladiumcontent of the crude product determined.

A 25 ml Radley's Carousel reaction vessel was charged with4-methoxyphenylboronic acid (0.26 g, 1.72 mmol, 1.5 eq),4-bromofluorobenzene (0.20 g, 1.14 mmol, 1 eq), potassium carbonate(0.47 g, 3.42 mmol, 3 eq) and 10 ml of IPA/H₂O (20:1). To this, themicroencapsulated palladium acetate catalyst System (3 mol %; weightsare as given in Table 3 below) was added.

TABLE 3 System 1A 1B 1C 2 3A 3B Amount of catalyst 0.07 0.07 0.07 0.090.07 0.07 added (g)

The mixture was stirred with a cross-shaped magnetic stirrer undernitrogen and heated to 85° C. using a Radleys Carousel reaction station.The progress of the reaction was monitored by taking samples of reactionmixture at regular time intervals and quantitatively analysing for theproduct by HPLC. After 22 hours the solid catalyst was removed byfiltration through a sintered funnel and the filtrate concentrated underreduced pressure (rotary evaporator) to remove the solvent. ICP analysisof the crude product was then performed. This procedure was repeated foreach System.

Results

The results of the ICP analysis are given in Table 4 below, which showsthe level of conversion to product at timed intervals using aquantitative HPLC method. The system of the invention (System 3) showslower levels of palladium residue in the crude product compared with theother Systems, indicating that the phosphine effectively bound to thepolyurea microcapsule matrix. Particularly when comparing System 3A withcomparative System 1A (both of which were obtained in the same manner,except for the presence of AIBN free radical initiator), it can be seenthat the use of a polymeric phosphine results in significantly lowerpalladium leaching. The reactivity of the catalyst of System 3 wascomparable with that of the other Systems.

TABLE 4 Time Conversion (%) at time (hours) 1A 1B 1C 2 3A 3B 0 0 0 0 0 00 1 51.1 42.3 57.9 72.2 46.2 44.4 3 79.4 72.7 76.2 74.6 70.5 73.3 5 84.581.2 89.7 82.0 81 6 87.7 83.6 95.9 88.1 94.8 22  93.6 89.4 99.2 98.399.6 98.1 Residual 30 — — 65 7 9 Pd in crude product (ppm)

Example 2

System 4 was obtained by reacting an amine-functional phosphine ligand,namely (diphenylphosphino)propyl-1-amine, with an isocyanate prepolymerto produce a polymeric ligand covalently attached to the final polyureamicrocapsule. Due to the air-sensitive nature of the ligand, the oilphase and microencapsulation process were maintained under inert (N₂)atmosphere.

Pd (OAc)₂ (1.30 g, 98%) was dissolved in chloroform (37 g) followed byaddition of 3-(diphenylphosphino)propyl-1-amine (1 g, 99%, 1:0.8 Pd/P)via a syringe and the resulting solution stirred for 10 min. To thismixture, polymethylene polyphenylene di-isocyanate (PMPPI) (15 g) wasadded and the contents stirred for a further 60 min under N₂ atmospherein a sealed screw-cap jar. The mixture was then added to a cooled (0-1°C.) aqueous mixture containing 40% REAX 100 M solution (10.86 g), 20%TERGITOL XD solution (5.43 g) and 25% Poly Vinyl Alcohol (PVOH) solution(8.69 g) in degassed deionised water (108 ml) while shearing (using aFISHER 4-blade retrieve-curve stirrer) at 500 rpm for 8 minutes. Theshear rate was then reduced to 250 rpm and after 60 min at 1° C. thebatch temperature was gradually allowed to warm to ambient temperature.A few drops of de-foamer (DrewPLus S-4382) were added during onsetpolymerisation to disperse the foam. The micro-emulsion thus obtainedwas stirred at room temperature for 24 h. The microcapsules were thenfiltered though a polyethylene frit (20 micron porosity) and the beadswashed in the following order: deionised water (5×100 ml), DMF (2×100ml), ethanol (3×100 ml), Toluene (2×100 ml) and hexane (3×100 ml). Thedark red-brown beads were then dried in a vacuum oven at 45° C. for 4hours.

Analytical Results:

ICP Analysis: 3.3% Pd wt/wt, Loading: 0.31 mmol/g (96% Pd encapsulated)

-   -   0.62% P wt/wt, Loading: 0.20 mmol/g (95% P encapsulated)

Particle size Distribution: 60-350 μm (average: 195 μm)

Example 3

Systems 5, 6 and 7 were obtained using nickel(II) β-diketone complexeswhich were reacted with an isocyanate prepolymer.

System 5

In System 5, a nickel(II) β-diketone complex was reactrf with theisocyanate in the prepolymer. As a consequence, the resultant organicphase was easily dispersed and converted into a stable microemulsion,producing good quality, useable microcapsules.

Nickel tetramethylheptanedionate (0.20 g, 0.47 mmol) was added to astirred solution of chloroform (2.6 g) under a nitrogen atmosphere.Toluene-2,4-diisocyanate (0.20 g, 1.00 mmol) was added and the solutionwarmed to 40° C. then allowed to cool to rt over 45 min to give a cleargreen solution. Polymethylene polyphenyl isocyanate (1.0 g, 2.71 mmol)was added and the solution stirred at 40° C. for a further 15 min.

An aqueous phase of water (8.4 g), 20% w/w Tergitol XD aq (0.50 g), 25%w/w PVOH aq (0.80 g) and 40% w/w Reax 100M aq (1.00 g) was made up in a50 ml round bottom flask with propeller form overhead stirring. Theorganic phase was dispersed via pipette over ca. 1 min into the stirred(460 rpm) aqueous phase. Stirring was continued at this speed for 5 minafter the start of oil phase addition, then shear reduced to 250 rpm.The microemulsion was stirred at rt for 1 h then at 40° C. for 14-18 h.After cooling, the polymer beads were filtered off and washed with water(4×50 ml) to give pale green beads.

System 6

In System 6, a nickel(II) β-diketone complex was reacted with anisocyanate before performing the microemulsion. The complex was onlypartially soluble in chloroform but after reaction with the isocyanatebecomes solubilised. After reaction with the isocyanate, the β-diketoneligand allowed a stable microemulsion to be formed by preventing thenickel from interfering with the stabilisation of the microcapsule. Themicrocapsules formed after dispersion had a high level of retention ofnickel.

Nickel acetoacetate (0.20 g, 0.78 mmol) was added to a stirred solutionof chloroform (2.75 g) under a nitrogen atmosphere.Toluene-2,4-diisocyanate (0.30 g, 1.50 mmol) was added and thetemperature of the resulting suspension raised to 40° C. After 2 hmixture had become a clear green solution, indicating the reactionbetween the isocyanate and acetoacetonate ligand had taken place. Aftercooling to room temperature polymethylene polyphenyl isocyanate (1.0 g,2.71 mmol) was added and the solution stirred at room temperature for afurther 1 h.

An aqueous phase of water (10.7 g), 20% w/w Tergitol XD aq (0.64 g), 25%w/w PVOH aq (1.02 g) and 40% w/w Reax 100M aq (1.28 g) was made up in a50 ml round bottom flask with propeller form overhead stirring. Theorganic phase was dispersed via pipette over ca. 1 min into the stirred(460 rpm) aqueous phase. Stirring was continued at this speed for 5 minafter the start of oil phase addition, then shear reduced to 250 rpm.The microemulsion was stirred at rt for 14-18 h then at 45° C. for 9 h.After cooling, the polymer beads were filtered off and washed with water(4×5 ml) then DMF (5 ml), IMS (2×5 ml), toluene (5 ml) and hexane (2×5ml) then vacuum dried at 40° C. for 4 h to give pale green beads (1.1 g,73%).

Nickel analysis by ICP showed 2.4% w/w Ni in the beads, corresponding toa loading of 0.41 mmol/g Ni (80% of target loading).

System 7

Nickel(II) bis(acetoacetonate) (1.20 g, 4.67 mmol) was added to astirred solution of chloroform (31 g) under a nitrogen atmosphere.Toluene-2,4-diisocyanate (1.95 g, 9.81 mmol) was added and thetemperature of the resulting suspension raised to 40° C. After 2 hours,the mixture had become a clear green solution, indicating the reactionbetween the isocyanate and acetoacetonate ligand had taken place.Polymethylene polyphenyl isocyanate (12.0 g, 32.5 mmol) was added andthe solution stirred for a further hour at room temperature, the mixtureremaining clear.

An aqueous phase of water (85.5 g), 20% w/w Tergitol XD aq (11.6 g), 25%w/w PVOH aq (13.8 g) and 40% w/w Reax 100M aq (17.3 g) was made up in ajacketed flange reactor with propeller form overhead stirring and warmedto 30° C. using a heater/chiller unit. The organic phase was dispersedvia a pressure equalised dropping funnel over ca. 1 min into the stirred(390 rpm) aqueous phase. Stirring was continued at this speed for 5 minafter the start of oil phase addition, then shear reduced to 240 rpm.The microemulsion was stirred at 30° C. for 14-18 h then at 45° C. for afurther 5 h.

After cooling, the polymer beads were filtered off and washed with water(4×50 ml) then DMF (2×25 ml), IMS 2×25 ml), toluene (25 ml) and hexane(2×25 ml) then vacuum dried at 40° C. for 4 h to give pale green beads(12.6 g, 83%).

1. A microencapsulated catalyst-ligand system comprising a catalyst and a ligand microencapsulated within a permeable polymer microcapsule shell, wherein the ligand is a polymeric ligand.
 2. A system according to claim 1, wherein the microcapsule shell is obtainable by interfacial polymerisation.
 3. A system according to claim 2, which is obtainable by a process comprising forming a permeable microcapsule shell by interfacial polymerisation in the presence of a catalyst and a ligand.
 4. A system according to claim 1, wherein the permeable polymer microcapsule shell is the product of self-condensation and/or cross-linking of etherified urea-formaldehyde resins or prepolymers in which from about 50 to about 98% of the methylol groups have been etherified with a C4-C10 alcohol.
 5. A system according to claim 1, wherein the permeable polymer microcapsule shell is a polyurea microcapsule prepared from at least one polyisocyanate and/or tolylene diisocyanate.
 6. A system according to claim 5, wherein the polyisocyanates and/or tolylene diisocyanates are selected from the group consisting of 1-chloro-2,4-phenylene diisocyante, m-phenylene diisocyante (and its hydrogenated derivative), p-phenylene diisocyante (and its hydrogenated derivative), 4,4′-methylenebis(phenyl isocyanate), 2,4-tolylene diisocyanate, tolylene diisocyanate (60% 2,4-isomer, 40% 2,6-isomer), 2,6-tolylene diisocyante, 3,3′-dimethyl-4,4′-biphenylene diisocyante, 4,4′-methylenebis (2-methylphenyl isocyanate), 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, 2,2′,5,5′-tetramethyl-4,4′-biphenylene diisocyanate, 80% 2,4- and 20% 2,6-isomer of tolylene diisocyanate, polymethylene polyphenylisocyante (PMPPI), 1,6-hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate and 1,5-naphthylene diisocyanate.
 7. A system according to claim 1, wherein the catalyst is an inorganic catalyst, preferably a transition metal catalyst.
 8. A system according to claim 7, wherein the catalyst is a transition metal catalyst, wherein the transition metal is platinum, palladium, osmium, ruthenium, rhodium, iridium, rhenium, scandium, cerium, samarium, yttrium, ytterbium, lutetium, cobalt, titanium, chromium, copper, iron, nickel, manganese, tin, mercury, silver, gold, zinc, vanadium, tungsten and molybdenum.
 9. A system according to claim 8, wherein the catalyst is a transition metal catalyst wherein the transition metal is palladium, preferably the palladium is in the form of an organic solvent soluble form and, for example, is palladium acetate.
 10. A system according to claim 1, wherein the ligand is obtainable by polymerisation of a ligand of formula (1): PR¹R²R³  (1) wherein: R¹, R² and R³ are each independently an optionally substituted hydrocarbyl group, an optionally substituted hydrocarbyloxy group, or an optionally substituted heterocyclyl group or one or more of R¹ & R², R¹ & R³, R² & R³ optionally being linked in such a way as to form an optionally substituted ring(s); and at least one of R¹, R² and R³ comprises a polymerisable group.
 11. A system according to claim 10, wherein at least one of R¹, R² and R³ comprises a styryl group.
 12. A system according to claim 11, wherein the ligand of formula (1) is selected from (4-styryl)diphenylphosphine, di-(4-styryl)phenylphosphine, tri-4-styrylphosphine, and corresponding 2-styryl and 3-styryl isomers thereof, (4-styryl)di-2-tolylphosphine, di-(4-styryl)-2-tolylphosphine, (4-styryl)di-2-tolylphosphine, di-(4-styryl)-2-tolylphosphine and corresponding 2-styryl and 3-styryl isomers thereof, allyldiphenylphosphine, diallylphenylphosphine, triallylphosphine, allydibutylphosphine, vinyldiphenylphosphine, divinylphenylphosphine, trivinylphosphine, and the following ligands:


13. A system according to claim 1, wherein the ligand is obtainable by polymerisation of a ligand comprising a cyclopentadienyl group.
 14. A system according to claim 1, wherein the ligand is obtainable by free radical polymerisation of a polymerisable ligand.
 15. A system according to claim 1, wherein the ligand is copolymerised with the microcapsule shell.
 16. A system according to claim 15, wherein the ligand is obtainable by copolymerisation of a polymerisable ligand comprising a hydroxy, amino or mercapto group; and a polyisocyanate.
 17. A system according to claim 15, wherein the ligand is obtainable by copolymerisation of a polymerisable ligand selected from β-diketones, β-ketoesters, β-ketoamides, β-dicarboxylic acids and derivatives thereof; and a polyisocyanate.
 18. A system according to claim 17, wherein the polymerisable ligand is selected from malonic acid and esters or amides thereof, malononitrile, cyanoacetic acid and esters or amides thereof, and acetoacetate compounds.
 19. A system according to claim 17, wherein the polymerisable ligand is complexed with a transition metal, for example, selected from Ni, Pd, Pt, Rh, Ru, as and Ir.
 20. A system according to claim 19, wherein the complex is a nickel (II)-β-diketone complex.
 21. A process for the preparation of a microencapsulated catalyst-ligand system, which comprises: (i) forming a microcapsule shell by interfacial polymerisation in the presence of a catalyst and a ligand; (ii) forming a microcapsule shell by interfacial polymerisation in the presence of a catalyst and treating the microcapsule shell with a ligand; or (iii) forming a microcapsule shell by interfacial polymerisation in the presence of a ligand and treating the microcapsule shell with a catalyst solution; wherein the ligand is a polymerisable ligand and the process further comprises polymerising the ligand prior to, during or after formation of the microcapsule shell.
 22. A process according to claim 21, which comprises forming a microcapsule shell by interfacial polymerisation in the presence of a catalyst and a ligand.
 23. A process according to claim 22, which comprises (a) dissolving or dispersing the catalyst and a ligand in a first phase, (b) dispersing the first phase in a second, continuous phase to form an emulsion, (c) reacting one or more microcapsule wall-forming materials at the interface between the dispersed first phase and the continuous second phase to form a microcapsule polymer shell encapsulating the dispersed first phase core, and optionally (d) recovering the microcapsules from the continuous phase.
 24. A process according to claim 21, which comprises forming a microcapsule shell by interfacial polymerisation in the presence of a catalyst and treating the microcapsule shell with a ligand.
 25. A process according to claim 24, which comprises (a) dissolving or dispersing the catalyst in a first phase, (b) dispersing the first phase in a second, continuous phase to form an emulsion, (c) reacting one or more microcapsule wall-forming materials at the interface between the dispersed first phase and the continuous second phase to form a microcapsule polymer shell encapsulating the dispersed first phase core, and (d) treating the microcapsules with a ligand.
 26. A process according to claim 21, which comprises forming a microcapsule shell by interfacial polymerisation in the presence of a ligand and treating the microcapsule shell with a catalyst solution.
 27. A process according to claim 26, which comprises (a) dissolving or dispersing the ligand in a first phase, (b) dispersing the first phase in a second, continuous phase to form an emulsion, (c) reacting one or more microcapsule wall-forming materials at the interface between the dispersed first phase and the continuous second phase to form a microcapsule polymer shell encapsulating the dispersed first phase core, and (d) treating the microcapsules with a solution of a catalyst.
 28. A process according to claim 21, wherein the interfacial polymerisation comprises self-condensation and/or cross-linking of etherified urea-formaldehyde resins or prepolymers in which from about 50 to about 98% of the methylol groups have been etherified with a C4-C10 alcohol.
 29. A process according to claim 21, wherein the interfacial polymerisation comprises condensation of at least one polyisocyanate and/or tolylene diisocyanate.
 30. A process according to claim 29, wherein the polyisocyanates and/or tolylene diisocyanates are selected from the group consisting of 1-chloro-2,4-phenylene diisocyante, m-phenylene diisocyante (and its hydrogenated derivative), p-phenylene diisocyante (and its hydrogenated derivative), 4,4′-methylenebis(phenyl isocyanate), 2,4-tolylene diisocyanate, tolylene diisocyanate (60% 2,4-isomer, 40% 2,6-isomer), 2,6-tolylene diisocyante, 3,3′-dimethyl-4,4′-biphenylene diisocyante, 4,4′-methylenebis (2-methylphenyl isocyanate), 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, 2,2′,5,5′-tetramethyl-4,4′-biphenylene diisocyanate, 80% 2,4- and 20% 2,6-isomer of tolylene diisocyanate, polymethylene polyphenylisocyante (PMPPI), 1,6-hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate and 1,5-naphthylene diisocyanate.
 31. A process according to claim 29, wherein a cross-linking reagent is present.
 32. A process according to claim 29, wherein unreacted amine groups are converted to urea, amide or urethane groups by post reaction with a monoisocyanate, acid chloride or chloroformate.
 33. A process according to claim 21, wherein the catalyst is an inorganic catalyst, preferably a transition metal catalyst.
 34. A process according to claim 33, wherein the catalyst is a transition metal catalyst wherein the transition metal is platinum, palladium, osmium, ruthenium, rhodium, iridium, rhenium, scandium, cerium, samarium, yttrium, ytterbium, lutetium, cobalt, titanium, chromium, copper, iron, nickel, manganese, tin, mercury, silver, gold, zinc, vanadium, tungsten and molybdenum.
 35. A process according to claim 34, wherein the catalyst is a transition metal catalyst wherein the transition metal is palladium, preferably the palladium is in the form of an organic solvent soluble form and most preferably is palladium acetate.
 36. A process according to claim 21, wherein the ligand is polymerised prior to formation of the microcapsule shell.
 37. A process according to claim 21, wherein the ligand is polymerised during formation of the microcapsule shell.
 38. A process according to claim 21, wherein the ligand is polymerised after formation of the microcapsule shell.
 39. A process according to claim 21, wherein the ligand is an organic moiety comprising one or more heteroatoms selected from N, O, P and S.
 40. A process according to claim 39, wherein the ligand is an organic ligand of formula (1): PR¹R²R³  (1) wherein: R¹, R² and R³ are each independently an optionally substituted hydrocarbyl group, an optionally substituted hydrocarbyloxy group, or an optionally substituted heterocyclyl group or one or more of R¹ & R², R¹ & R³, R² & R³ optionally being linked in such a way as to form an optionally substituted ring(s); and at least one of R¹, R² and R³ comprises a polymerisable group.
 41. A process according to claim 39, wherein at least one of R¹, R² and R³ comprises a styryl group.
 42. A process according to claim 40, wherein the ligand of formula (1) is selected from (4-styryl)diphenylphosphine, di-(4-styryl)phenylphosphine, tri-4-styrylphosphine, and corresponding 2-styryl and 3-styryl isomers thereof, (4-styryl)di-2-tolylphosphine, di-(4-styryl)-2-tolylphosphine, (4-styryl)di-2-tolylphosphine, di-(4-styryl)-2-tolylphosphine and corresponding 2-styryl and 3-styryl isomers thereof, allyldiphenylphosphine, diallylphenylphosphine, triallylphosphine, allydibutylphosphine, vinyldiphenylphosphine, divinylphenylphosphine, trivinylphosphine, and the following ligands:


43. A process according to claim 39, wherein the ligand comprises a cyclopentadienyl group.
 44. A process according to claim 21, wherein the ligand is polymerised by free radical polymerisation.
 45. A process according to claim 21, wherein the ligand is copolymerised with the microcapsule shell or a constituent (e.g. a monomer or prepolymer) thereof.
 46. A process according to claim 45, wherein the ligand comprises a hydroxy, amino or mercapto group and the microcapsule shell or constituent thereof comprises a polyisocyanate.
 47. A process according to claim 45, wherein the ligand is selected from β-diketones, β-ketoesters, β-ketoamides, β-dicarboxylic acids and derivatives thereof; and the microcapsule shell or constituent thereof comprises a polyisocyanate.
 48. A process according to claim 47, wherein the ligand is selected from malonic acid and esters or amides thereof, malononitrile, cyanoacetic acid and esters or amides thereof, and acetoacetate compounds.
 49. A process according to claim 47, wherein the ligand is complexed with a transition metal, for example, selected from Ni, Pd, Pt, Rh, Ru, as and Ir.
 50. A process according to claim 49, wherein the complex is a nickel (II)-β-diketone complex.
 51. A microencapsulated catalyst-ligand system obtainable by a process of claim
 21. 